Stabilized tetrachloroethylene composition



Patented Sept. 11, 1951 STABILIZED TETRACHLOROETHYLENE. COMPOSITION Maxwell J. Skeeters, Fairport Harbor, and William J. Esselstyn, Painesville, Ohio, assignors to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware No Drawing. Application May 23, 1950, Serial No. 163,802

8 Claims.

This invention relates to inhibiting the decomposition of tetrachloroethylene catalyzed by light, air, heat, moisture, and metal surfaces and more particularly relates to a composition of matter consisting essentially of tetrachloroethylene and stabilizing amounts of lower nitroalkanes and chloro-derivatives thereof.

It has heretofore been known that tetrachloroethylene (perchloroethylene) of a high degree of purity and containing only minute amounts of saturated, or other unsaturated, lower aliphatic chloro-hydrocarbons is very inert to the action of air, light, heat, moisture, and metal surfaces with which it comes into contact during storage and commercial use. However, the obtaining of such high purity tetrachloroethylene in commercial production is not generally feasible and it has been found thatthe impure material normally encountered in commerce decomposes when in contact with the substances noted above. Hence, means other than purification for preventing or inhibiting the decomposition of tetrachloroethylene and the lower chlorinated aliphatic hydrocarbons generally associated therewith must be had.

It is generally believed that tetrachloroethylene exposed to air, light, heat, moisture,

etc., decomposes, especially in the presence of.

moisture, principally by way of oxidative. attack at the double bond involving a series of steps in which the ultimate products include phosgene, trichloroacetic acid, and hydrogen chloride. It is also believed that the oxidative attack is catalyzed by light and by the products of oxidation, as a result of which, oxidative decomposition once initiated is self-catalyzing and self-sustaining. Other chloro-hydrocarbons generally associated with crude commercial tetrachloroethylene also are subject to oxidative attack and decompose to some of the same products as those formed by the oxidation of tetrachloroethylene, and at a somewhat accelerated rate, as compared to the oxidation of tetrachloroethylene. These products are then available to catalyze the, decomposition of the tetrachloroethylene. For example, tetrachloroethylene obtained commercially from the crude products of chlorination and chlorinolysis of lower aliphatic hydrocarbons may contain small but appreciable amounts of saturated and unsaturated chlorinated hydrocarbons, such as dichloroethylene, trichloroethylene, trichloroethane, unsymmetrical tetrachloroethane, pentachloroethane, and the like. These lower chlorohydrocarbons in themselves are relatively innocuous in solvent 7 extraction processes in which the tetrachloroethylene is used, but the oxidation decomposition products thereof corrode metal surfaces with which a body of tetrachloroethylene containing them comes into contact. These less stable chloro-hydrocarbons are believed to be the principal initial source of chloro-oxygen-containing impurities, such as phosgene, chloroacetic acid, trichloroacetic acid, and the like, in the tetrachloroethylene, which impurities catalyze decomposition of the tetrachloroethylene.

The problem, therefore, is principally one of inhibiting the initiation of the oxidation of the chlorohydrocarbons commonly associated with commercial tetrachloroethylene, as well as inhibiting the oxidation of tetrachloroethylene itself.

One of the objects of the present invention is to provide means for inhibiting oxidation of tetrachloroethylene and lower aliphatic chlorohydrocarbons generally associated therewith during exposure to air, light, heat, moisture, and metal surfaces.

Another object of the invention is to provide a procedure for treating and purifying crude tetrachloroethylene in order to obtain maximum efliciency of the stabilizer in the purified product.

These and other objects will be apparent to those skilled in the art from the discussion hereinafter. 1

It has now been found that where crude tetrachloroethylene, particularly that obtained from commercial processes involving the chlorinolysis of lower hydrocarbons or hydrocarbon chlorides, or the chlorination and simultaneous dehydrochlorination of hydrocarbon chlorides, such as ethylene dichloride, or of unsaturated hydrocarbons, such as acetylene, ethylene, ethane, and the like, contains appreciable amounts of chlorinated lower aliphatic hydrocarbons other than tetrachloroethylene as impurities, such crude product may initially be treated with an aqueous solution of an inorganic base and a high boiling point organic base in order to destroy the major portion of volatile acids and acid-forming impurities, and then combined with lower nitroalkanes, or chloro-derivatives thereof, whereby decomposition of the tetrachloroethylene and other lower chlorinated aliphatic hydrocarbons is inhibited under the most adverse conditions of storage and commercial use.

In general, the present invention is directed to a composition consisting essentially of tetrachloroethylene and stabilizing amounts of a compoundof the general formula.

wherein R. is selected from the group of hydrogen, methyl, and ethyl; R is selected from the: group of hydrogenand methyl, and is hydrogen when R is ethyl; and X is selected from the group of hydrogen and chlorine, and is hydrogen when R and R are hydrogen.

Thus, the generic formula defines the nitroderivatives of methane, ethane and propane, and the nitro-chloro-derivatives of ethane and propane in which the chlorine atom is attached to the carbon atom bearing the nitro-group. These compounds have been found particularly effective in stabilizing tetrachloroethylene contaminated with minor amounts of other lower aliphatic chloro hydrocarbons, both in the liquid and in the vapor phase. The stabilizing effect has been found enhanced by pre-treatment of the tetrachloroethylene which removes or destroys the greater part. of the impurities, such as hydrogen chloride, phosgene, and the chloro-acids, prior to combining it with the stabilizer.

The initial treatment of the crude tetrachloroethylene may include adding an organic base of the amine type and having a boiling point substantially higher than tetrachloroethylene, for example, aniline inan amount from approximately 02-20% by weight to the crude product, and fractionally distilling the crude mass to recover substantially all of the tetrachloroethylene as an intermediate fraction in the distillation; additional treatments may include Washing the tetrachloroethylene fraction with a solution of an inorganic base, such as an alkali metal or alkaline earth metal base, for example, sodium. hydroxide, sodium carbonate, calcium hydroxide, magnesium bicarbonate, and the like, drying the washed product and distilling the dried product to recover a more highly refined tetrachloroethylene fraction. The purpose in using an amine, such as aniline, is to allow for the reaction of such amine, with acid chloride products contained in the crude product, whereby an anilide or analogous compound may form during distillation and the undesired impurity is retained in the distillation residue. The purpose of washing the effluent from the initial distillation with an alkali, metal or alkaline earth metal base is to remove the more volatile of the acid chloride impurities, such as hydrogen chloride, phosgene, and the like, which may not have reacted with the amine.

The crude product may also be washed initially with a solution of an inorganic base, such as those noted above, dried, and combined with an amine having a boiling point substantially higher than tetrachloroethylene, generally in an amount from 0.22.0% by weight, and the mixture thus obtained distilled as described above in order to recover the purified tetrachloroethylene substantially free from chloro-oxygen-containing impurities.

Where such impurities as hydrogen chloride, phosgene, chloro-acids and the like, are known to be extremely low in the crude product, this material may be combined with an amine such as aniline, as noted hereinabove, and subjected to fractional distillation torecover the substantially pure tetrachloroethylene without the necessity of resorting to the treatment with a solution. of n inorganic base. Moreover, the dilute alkaline wash may be omitted even where the chloro-oxygencontaining compounds are present in appreciable treatments, the recovered tetrachloroethylene' may be combined with a stabilizing amount of the lower nitroalkanes or chloro-derivatives thereof noted above, for example, in an amount from 0.0l1.0% by Weight of tetrachloroethylene, pref erably, however, from 02-03% where the above rare-treatments or their equivalent have been used. The extremes within the above-noted broad range are preferred where the amount of chloro-hydrocarbon impurities associated with the tetrachloroethylene is unusually high or unusually low, while the amounts within the intermediate preferred range are generally sufiiciently effective where the purified tetrachloroethylene contains not more than about 1 3% of the lower chlorinated aliphatic hydrocarbon impurities consisting essentially, of trichloroethylene, the most common impurity obtained in commercial production.

The beneficial effects of the present invention may also be realized where tetrachloroethylene has been purified in a commercial operation and stabilized either with a high. boiling point stabilizer, i. e., a stabilizer such as one of the amine or of the ether type having a higher boiling point than that of tetrachloroethylene, or with stabilizers which are more volatile than tetrachloroethylene, by removing such stabilizer as by chemical reaction, azeotropic distillation, or the like; the thus-treated mass is then fractionally distilled to recover the tetrachloroethylene fraction, which may be combined with amember of the group of nitroalkanes and chloro-derivatives thereof, noted hereinabove, in an amount suflicient to effect stabilization, whereby the tetrachloroethylene is rendered especially suitable, due, to, its stability, for degreasing or dry cleaning operations.

In order that those skilled in the art may better understand the present inventionand in what manner the same may be, carried into effect, the following specific examples are offered:

Example I A mixture of chloro-hydrocarbons containin tetrachl'oroethylene, trichloroethylene, unsymmetrical tetrachloroethane, symmetrical tetrachloroethane, pentachloroethane, and hexachloroethane is subjected to fractional distillation to separate a light fraction, a substantially pure tetrachloroethylene fraction, and leave a residue of higher boiling chloro-hydrocarbons. Two 25-ml. portions of the tetrachloroethylene are placed in round-bottom, one-neck flasks, together with 0.8 ml. of water, and strips of aluminum, foil. To one of these. portions of tetrachlo'roethylene thereis added 0.1 ml. of l-nitropropane (0.25% by weight) as a stabilizer for the tetrachloroethylene. The flasks containing the tetrachloroethylene and other ingredients are at,- tached to reflux condensers and the contents of the flasks heated at the reflux temperature for a period of 24 hours, while exposed to the light radiation from a IOU-watt incandescent lamp. At the e d of the 24-hour reflux period, the pieces of aluminum foil are removed from the, flasks, washed, dried, and weighed. The change, in Weight of both piece Qf, aluminum foil, less tracts titrated with 0.02 N silver nitrate solution according to the Volhard method for the determination of the chloride ion. Analysis of the aqueous extract of the sample to which no stabilizer has been added shows that the tetrachloroethylene at the end of the 24-hour reflux period contains 0.038 gm. of chloride, calculated as Cl, per liter. In the same manner, the portion of tetrachloroethylene containing the nitropropane as a stabilizer is found to contain 0.012 gm.

of chloride, calculated as Cl, per liter.

Example II I A crude mixture of lower chlorinated aliphatic hydrocarbons obtained from a commercialunit for the production of tetrachloroethylene and trichloroethylene is vaporized and the vapors passed through activated carbon particles at a temperature within the range of 250-280 C. The

effluent vapors from this thermal treatment are condensed and subjected to fractional distillation. To one of two -ml. portions of this tetrachloroethylene fraction, taken for test according to the procedure of Example I, there is added 0.25% by weight of l-nitropropane (0.10 ml.), 0.8 ml. of water, and a weighed strip of aluminum foil. To the other 25-1111. portion there is added 0.8 ml. of water and a weighed aluminum strip. The contents of both flasks are heated to the reflux temperature for tetrachloroethylene for a period of 24 hours, processed as described in Example I. and the following results obtained:

Example III Crude tetrachloroethylene obtained from a commercial production unit is washed with a dilute solution of caustic soda and soda ash in a separatory funnel, the aqueous and nonaqueous phases separated, and the crude tetrachloroethylene dried over anhydrous calcium chloride. The dried material is then combined with 0.25% by weight of aniline and subjected to fractional distillation. The 100-ml. portions of the refraction-ated material are each combined with 0.25% by weight (0.4 ml.) of l-nitropropane and placed in round-bottom, one-neckflasks. A piece of copper foil (1) weighing 0.7092 gm. is placed in one of the flasks, together with 0.2 ml. of water. This flask is then attached to a Soxhlet extractor containing a piece of copper foil (2) weighing 0.6742 gm. and. this set-up attached to a reflux condenser having a piece of copper foil (3) Weighing 0.7007 gm. inserted at the vapor inlet thereto and extending upwardly therein to the condensing surfaces. The pieces of copper foil inserted in the second apparatus in the same places as thos strips in the first apparatus Weigh 0.6302 gm. (in the flask), 0.6015 gm. (in the Soxhlet extractor), and 0.6491 gm. (in the condenser). The tetrachloroethylene is heated to boiling and maintained at the boiling temperature for a period of 72 hours, while exposed to light radiation from a 100-w. incandescent lamp. At the end of the 72-hour period, the copper strips are removed from the apparatus, washed, dried, and weighed. The contentsof the flasks are extracted with distilled water and the extracts titrated with 0.10 N sodium hydroxide solution to determine the acidity, and the following results are obtained:

Acidity H2O x ract Copper Foil Strips (3) Two samples of tetrachloroethylene from the same batch as that described in the test above are subjected to the reflux test described in Example I above and the amount of chloride, calculated as Cl, per liter in the tetrachloroethylene at the end of the 24-hour reflux period arefound to be 0.006 gm. and 0.004 gm. respectively.

Example IV A batch of crude lower chloro-hydrocarbons obtained from a commercial unit for the production of tetrachloroethylene and trichloroethylene is allowed to stand for a period of about 18 days. This crude material is washed with 20% caustic soda. solution, dried over calcium chloride, and the dried material combined with 1% by Weight of aniline prior to distillation. The tetrachloroethylene recovered from the distillation is washed with 10% caustic soda solution and dried over calcium chloride. The dried product is divided into four portions; to the first portion there is added 0.25% by weight of l-nitropropane; to the second, 0.25% by weight of nitroethane; to the third, 0.25% by weight of nitromethane; and the fourth is without added stabilizer, as a control. mls. of each portion are placed in roundbottom flasks and subjected to the stability test described in Example III above, with the following results:

gi; of Loss in Weight Sample Stabilizer Extracgv 953 g zjg V Strips (3) l-Nitropropane 3. 9 9. 7 Nitroethane. 7. 1 16. 4 N itromethane l0. 4 l3. 7 Control 230. 2

1 More than 250 mls.

Example V 121 c. is washed with 10% NazCOa solution, dried by passing the washed material through anhydrous calcium chloride, and a 25-ml. portion thereof placed in each of three round-bottom flasks. To one of the flasks (labeled #1) is added 0.10 ml. of l-nitropro-pane, 0.8 ml. of water, and a weighed strip of aluminum foil. To a second flask (labeled #2) is added 0.084 ml. of 2-chlorothe Volhard method) Gms O1 Liter Gain or Loss 1n simpe ow salsa...

Less than 1 mg... 0.003 d 0.003 do 0. 006

While there have been described various embodiments of the invention, the products described are not intended to be understood as v limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its Principle may be utilized.

What is claimed is:

1. A composition of matter consisting essentially o1" tetrachloroethylene and a stabilizing amount of a compound of the general formula wherein R is selected from the group of hydrogen, methyl, and ethyl; R is selected from the group of hydrogen and methyl, and is hydrogen when R. is ethyl; and. X is. selected from the group of hydrogen and chlorine, and is hydrogen when R and R are hydrogen.

2. A composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of a chloro-nitroalkane of the general formula wherein R is selected from the group of hydrogen, methyl, and ethyl, and R is selected from the group of hydrogen and methyl, and is hydrogen when R is ethyl.

3. vA composition of matter consisting essentially of tetrachloroethylene and a stabilizing amount of a nitroalkane of the general formula R\ /N01. R H

wherein R and R have the significance ascribed in claim 1.

4. The composition of claim 3 in which the nitroalkane is nitromethane.

5. The composition of claim 3 in which the nitroalkane is nitroethane.

6. The composition of claim 3 in which the nitroalkane is l-nitropropane;

7. The composition of claim 2 in which the chloro-nitroalkane is l-chloro-l-nitroethane.

8. The composition of claim 2 in which the chloro-nitroalkane is 2-chloro-2-nitropropane. MAXWELL J. SKEETERS. WILLIAM J. ESSELSTYN.

REFERENCES CITED Number Name Date Klabunde Feb. 24, 194a 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF TETRACHLOROETHYLENE AND A STABILIZING AMOUNT OF A COMPOUND OF THE GENERAL FORMULA 